not too far away... and yes you can do a staggered harvest... cut the tops off, then let the rest ripen a bit more.. perfectly okay to do that. Adjust lights to new canopy height too.
Trichomes -- 10-100% amber depending on personal preference, you can see there's a large window here.
Pisitils -- coloration shuld be nearly 100%, though some plants may only be 50/50 colored pistils.
density -- colas should feel dense -- don't do this until the last thing to verify... squeezing colas isn't a good thing.. so don't do this until it's the last thing you check and only to be certain of the choice.
Use all three and you'll more consistently choose a specific point to harvest... with consistency you can try more/less amber and how that impacts the buzz...
more amber tends to make you sleepier, but all weed when youcome down should make you tired, as it is a stimulant ( temporarily increases metabolism / heart bpm etc) when yuo come "down" you crash like any other stimulant, but it's not a steep hill like meth or coke, LOL.